This application claims the priority of German patent document 103 03 347.5, filed Jan. 29, 2003, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and to a circuit for changing an analog actual signal to a digital desired signal.
RF systems are known which have RF (radio frequency) amplifiers as detectors (e.g., rf detectors or current sensors) for monitoring the transmitting and receiving operation. In this case, a detected video signal is an image of received rf pulses, which are monitored by analog comparators and compared with a reference threshold. The output of these comparators is analyzed, and the result is normally forwarded by way of serial interfaces for further processing.
Referring to FIG. 1, the (normally programmable) analog comparator K generates the reference threshold (the analog desired signal ASS) internally by means of an installed digital-to-analog converter D/A. The corresponding digital values DSS for the analog desired signal ASS are stored in a known storage medium SP, such as an EPROM and, depending on the operating mode of the comparator K, are written into the corresponding comparator input 1. The analog actual signal SI is fed to the other comparator input 2. At the comparator output A, it can be determined whether the actual signal SI is larger or smaller than the desired signal ASS (FIG. 1).
For calibrating the detectors, the rf power to be monitored is measured, for example, by means of an RF power meter (the so-called Peak Power Analyzer). Simultaneous, for the same rf pulse, the detected voltage must be measured at the detector, normally by means of an oscilloscope, at the output pin of the respective comparator.
The high construction cost and time expenditures required for the measuring operation at the comparator output as described above are disadvantageous. Normally, no test pins or external plug connections are available at the output of the comparator, because this requires considerable additional expenditures during the production. Thus, for testing purposes, the entire apparatus must be reconstructed (for example, opened) in order to detect the actual signal at the comparator input. This creates measuring uncertainties because of tolerances at the measuring point in time by means of the oscilloscope, and measuring faults as a result of, for example, coupled-in interferences which falsify the actual signal. These measuring uncertainties therefore lead to disadvantages during the calibration of the detectors.
Other disadvantages result from the fact that certain detectors may have to be calibrated at different temperatures and thus in climatic test chambers, making the adaptation of the test signals more difficult.
It is an object of the invention to provide a simple, rapid, substantially automatic method for changing an analog actual signal to a digital desired signal.
Another object of the invention is to provide such a method, by which an adaptive calibration of detectors becomes possible.
Still another object of the invention is to provide a circuit for implementing the method.
These and other objects and advantages are achieved by the method and apparatus according to the invention, in which the digital input signal fed to the digital/analog converter is adapted as a function of the output signal of the comparator present at the comparator output in a definable number of iterative steps (between definable lower and upper thresholds) according to a balancing method. The digital input signal fed to the digital/analog converter corresponds to the digital desired signal to which the analog actual signal is conformed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.